The Phoenix lander's search for Martian life evidence will begin in earnest this week as the spacecraft's organic chemistry instrument is fed a sample of 100% water ice. The mission team also wants to do ice sampling as early as possible, in the event an electrical short in the device prematurely halts organic-oven operations.

The ice sample is to be processed starting about July 9, with results due about July 15.

This marks a major shift in mission emphasis - from the general characterization of the landing site to specific, focused testing of ice and the soil/ice interface region. This change is being done for "good news" and "bad news" reasons.

First, the robotic arm has finally uncovered and prepared a large area of ice near the lander that makes such sampling possible. The bad news is that there's some urgency because of concerns about an electrical short in the Thermal and Evolved Gas Analyzer (TEGA) organic chemistry instrument (AW&ST June 30, p. 37).

The short developed when TEGA's soil screen shaker mechanism was operated several times to break up clumpy soil that initially would not fall into one of eight ovens. Now the objective is to obtain a guaranteed ice sample in case the short worsens and TEGA dies.

"We are treating the next sample to TEGA as possibly our last," says Peter Smith of the University of Arizona (UA). As overall principal investigator, he heads the Phoenix program.

It boils down to conservative sample planning, because managers believe the instrument could continue to work. But they're also hedging their bets since a key factor is that the shaker mechanism always operates when TEGA takes in a sample, as it will do with the ice. Shaking can worsen the short-circuit problem.

Jet Propulsion Laboratory (JPL), Lockheed Martin and UA engineers are assessing the options to bias TEGA toward continued operations.

On the science side, the NASA Mars program has stressed for years the "follow the water" theme in the search for evidence of Martian life. By sampling the water ice, lander instruments will finally be able "to taste the water," as Ed Weiler said May 25, the day Phoenix landed. He heads NASA's science mission directorate.

This week's operations are taking place just days after the lander's wet chemistry instrument found that the soil composition at the landing site is Earth-like and chemically favorable for supporting life - if there is any life there now or had been in the past (AW&ST June 30, p. 37).